A mobile device, such as a smartphone, tablet computer, etc., has a screen that allows a user to navigate web pages, watch videos, or perform other activities. However, conventional mobile devices have a fixed size screen such that the size of the screen cannot be varied according to the user's different activities. For example, it may be more convenient to use only a small screen mobile device when the user navigates web pages, but a large screen mobile device would provide a better watching experience when the user watches videos.